It is often desirable to equip motor vehicles with protective devices as a supplement to or as a replacement of safety belts. For example, it is already known to arrange knee protective devices in the vehicle instrument panel in combination with airbags for the driver as well as for the passengers. The knee protective device may be constructed so as to comprise energy absorbing material which is placed behind or which forms an integral part of the instrument panel. This type of knee protective device is, however, conditioned on the existence of a comparatively large zone of deformation behind the instrument panel, a feature which it may be difficult to obtain in small and compact cars. For this reason it is desirable that the energy absorption is initiated already before the knees reach the instrument panel.
This goal may be achieved by means of active knee protective systems wherein a required deformation path is created by a load-absorbing plate which is rapidly propelled against the knees through the deployment of an airbag, whereupon the kinetic energy of the knees in the forwards direction is decelerated (absorbed) by the return movement of the plate as the airbag deflates.
One kind of airbag of this type, devised for being housed in a vehicle instrument panel, is disclosed in EP 0 684 164 A1. This airbag device comprises a panel door which is removable in its entirety from the rest of the surrounding panel. An airbag module comprising an airbag and a gas generator is positioned behind the panel door. As a result of the activation of the airbag and the subsequent deployment thereof, the panel door is urged outwards, away from the rest of the panel, into contact with the knee of the vehicle occupant. One problem found in this type of airbag arrangements is, however, the gap formed in the joint between the panel door and the surrounding panel, which detracts from the aesthetic appearance of the vehicle interior.
U.S. Pat. No. 5,035,444 describes a similar airbag device the panel door of which is pivotally attached to the surrounding panel along part of its circumference. Owing to this arrangement the panel door will be pivoted upwards as the airbag behind is inflated. In order to hide the joint between the panel door and the surrounding panel the publication suggests the provision of a surface cover on the panel. The surface cover is adapted burst or rip open as the panel door pivots upwards, to allow expansion of the airbag. However, also this latter type of airbag device causes problems in that the airbag, when deployed, is exposed to the vehicle occupant, resulting in dust and other particles entering into the vehicle compartment and being given considerable kinetic energy owing to the very rapid expansion of the airbag. In addition, these airborne moving particles are a potential source of danger as they may cause personal injuries.